Olfactory and vomeronasal sensory inputs to the limbic system are essential for the initiation of mating behavior in male hamsters. Altered sexual behavior after manipulations of these inputs has been documented, but the neuroanatomical substrate for chemosensory control of mating is unknown. Research proposed here is designed to determine the neuronal pathways which originate from the olfactory terminal fields in the primary olfactory cortex, olfactory tubercle, entorhinal cortex, and anterolateral part of the corticomedial amygdala, and from the entirely segregated vomeronasal fields in the posteromedial part of the corticomedial amygdala and bed nucleus of the stria terminalis. In addition to defining these projection systems, attention will be given to elucidating the pattern of convergence of olfactory vomeronasal inputs with other afferents in selected forebrain integration centers, including the amygdala, frontal cortex, entorhinal cortex, and bed nucleus of the stria terminalis. Efferent projections will be traced with autoradiography of transported proteins after injections or iontophoresis of tritiated amino acids, and with silver impregnation of degenerating terminals after destruction of cell bodies. The origins of afferent pathways to a brain area will be identified with injections or iontophoresis of horseradish peroxidase (HRP) which is localized histochemically after retrograde transport from neuron terminals at the site of injection, back to their cell bodies. HRP will be used here as a means of identifying convergent inputs to a given region and also for refining information about efferent pathways. The behavioral significiance of these central olfactory and vomeronasal areas will then be studied by observing mating behavior in male hamsters after bilateral lesions of selected parts of the pathways.